1. Field of the Invention
The present invention relates to a magneto-resistive head, and more particularly, to a magneto-resistive head of a new structure which provides a linear output according to variation of a recording magnetic flux.
2. Description of the Related Art
An existing inductive head adopts a method for converting a variation of a magnetic flux on a disk into a variation of a voltage in a head coil, using a head core wound with a coil. In this inductive head, if the frequency of a data signal becomes high, the inductance of the head coil should be lowered to maintain stability of the data signal. This causes an induced voltage of the head to be lowered, and finally detection of the data signal to be unstable.
A magneto-resistive head (hereinafter, referred to as MR head) is provided for solving the above problem. The MR head has an MR sensor for easily detecting variations of a magnetic flux when the data signal has a high frequency. The MR head converts variations in magnetic flux into variations in resistance, using the MR sensor, when a data read is performed, but records data with an existing inductive head when a data write is performed, to enable a signal-to-noise ratio to be improved.
FIG. 1 shows the structure of a conventional general MR head. See U.S. Pat. No. 5,828,528 to Charles H. Tolman et al. entitled MR Sensors With Selected Resistances For The Sensing And Biasing Layers To Enhance Reading Capabilities, incorporated herein by reference. In FIG. 1, an MR element 10 is isolated from a soft adjacent layer (SAL) 12 by a spacer 14. The MR element 10 is disposed in such a manner that the forward (easy) direction of the MR element 10 parallels the direction of width of a track.
A bias magnetic flux Hb is applied via the SAL 12, in order to avoid non-linearity when the easy direction of the MR head 10 is horizontal. The bias magnetic flux Hb forms a predetermined angle with respect to the easy direction magnetic flux He. This angle can be adjusted by adjusting the thickness and constituent ratio of the SAL 12.
The resistance of the MR element 10 is modulated by the flux of data recorded on a medium. Here, the easy direction of the MR element 10 means a direction of varying the resistance of the MR element 10 with respect to variations of the magnetic flux.
When a measured current flowing through the MR element 10 is I, the output voltage of the MR element 10 equals a value obtained by multiplying the varied resistance by the measured current according to Ohm's law.
That is, .DELTA.V=I.DELTA.R.
FIG. 2 is a graph showing the resistance characteristics in the FIG. 1 apparatus. In FIG. 2, the X axis denotes the easy direction magnetic flux He, and the Y axis denotes the recording magnetic flux Hy. The recording magnetic flux Hy moves to the upper or lower direction assuming the magnitude is the same.
A vector angle of a composite magnetic flux formed by composition of the recording magnetic flux Hy and the bias magnetic flux Hb varies as the direction of the recording magnetic flux Hy varies.
In this case, the resistance of the MR element is determined as follows. EQU .rho.=.rho..sub.0 +.DELTA..rho.cos.sup.2.theta. (1)
in which .rho. denotes a specific resistance of the MR element 10, .DELTA..rho. denotes a maximum value of variation of the specific resistance, and .theta. denotes an angle between the easy direction magnetic flux He and the composite magnetic flux.
The maximum value of the resistance variation is generated when .theta. equals 0.degree. and the minimum value is generated when .theta. equals 90.degree.. The resistance variation according to the direction of the recording magnetic flux is symmetrical when .theta. equals 45.degree.. Thus, if the bias magnetic flux Hb forms an angle of 45.degree. with respect to the easy direction magnetic flux He, a substantially linear resistance characteristic is obtained with respect to the variation of the recording magnetic flux.
In FIG. 2, when the directions of the composite magnetic fluxes with respect to the recording magnetic fluxes Hy and -Hy are .theta.' and .theta.'", the specific resistance varies to .rho.' and .rho.'", respectively. Also, .theta.' and .theta." are symmetrical with respect to an angle of 45.degree., (.rho.'-.rho.p") and (.rho."-.rho.'") are approximately equal.
However, as can be seen from the equation (1), the variation of the output signal according to the recording magnetic flux Hy is not fundamentaly linear, which causes a problem of asymmetry. That is, in FIG. 2, (.rho.'-.rho.") and (.rho."-p'") are not substantially equal. asymmetry problem causes a processor to generate an error when a signal recorded on a disk is read out from an output of the MR element 10.